若tanα-1/2tanα+1=1,且α∈(π,3π/2),则cos α= 谁会啊，详细点

显示全部楼层 · 2012-4-27 17:07:00

tanα-1/2tanα+1=1tana-1=2tana+1tana=-2所以sin2a/cos2a=45cos2a=1cos2a=1/5因为 α∈(π,3π/2),cosa<0cosa=-√5/5...

千问 · 2012-4-27 17:07:00

[tanα-1]/[2tanα+1]=1tana-1=2tana+1tana=-2,且α∈(π,3π/2),则cos α<0tana=sina/cosa=-2sina=-2cosa(sina)^2+(cosa)^2=15(cosa)^2=1cosa=-根号5/5...

千问 · 2012-4-27 17:07:00

(tanα-1)/(2tanα+1)=1tanα-1=2tanα+12tanα-tanα=-1-1tanα=-2∵α∈(π,3π/2),在第三象限∴cosα=-1/√[(tanα)^2+1]=-√5 /5...

千问 · 2012-4-27 17:07:00

tanα-1/2tanα+1=1tana-1=2tana+1tana=-2sin2a/cos2a=45cos2a=1cos2a=1/5cosa<0cosa=-√5/5...